U.S. Pat. No. 5,147,830, issued to Banerjee and Connors, Jr., discloses a pumpable refractory casting composition used for forming new liners, and repairing existing liners, in molten metal containment devices. The pumpable refractory composition replaced earlier refractory compositions which were not pumpable and had to be transported using buckets and cranes. The uses for the pumpable refractory composition include, but are not limited to, tundishes, ladles, troughs, runners, blast furnaces, and other molten metal containment devices.
The compositions disclosed in U.S. Pat. No. 5,147,830 include, as a primary ingredient, 55-90% by weight of a refractory base material which can be calcined clay, mullite, brown fused alumina, tabular alumina or combinations thereof. All of these base materials include significant amounts of alumina. Calcined clay includes about 43-48% by weight alumina. Mullite includes about 57-73% by weight alumina. Brown fused alumina includes about 93-98% by weight alumina, and tabular alumina includes about 98.5-99.9% by weight alumina.
The compositions disclosed in U.S. Pat. No. 5,147,830 also include a colloidal silica binder, and may include other refractory ingredients (e.g. silicon carbide, graphite, microsilica) and a setting agent. The colloidal silica, in addition to serving as a binder, contributes excellent flow properties which facilitate the pumping of the casting composition during its application.
Many metal containment devices, for example, blast furnace runners and troughs, contain molten metal which includes some impurities. These impurities tend to float to the top of the molten metal, forming what is called a "slag" layer. The slag layer typically includes non-metallic impurities, many of which are oxidized or oxidizable, and reactive gases such as entrained oxygen or air.
Impurities in the slag layer react with the alumina and any carbon in the refractory liner, causing oxidation of carbon and general weakening of the liner. As a result, the portion of the refractory liner which is adjacent to the slag layer wears out faster than the remaining refractory liner, accelerating the time at which the refractory liner must be repaired or replaced. Therefore, there is a need or desire in the iron and steel industry for a refractory material which is especially resistant to attack from slag, and which can be used in refractory liners in regions exposed to slag.